This invention relates to a liquid crystal display device containing a nematic or cholesteric liquid crystal horizontally oriented in advance, where the orientation of a liquid crystal molecule is changed by applying an electric field, a magnetic field, heat or the like to the device and changing the intensities of the electric field, magnetic field, heat or the like, and more particularly to an alignment film of such a liquid crystal display device.
A liquid crystal display device is basically in such a structure that a pair of glass substrates are arranged in parallel at a specific distance, and a transparent, electroconductive film is selectively deposited on each of counter-faced sides of the pair of substrates, where these electroconductive films and glass surfaces are completely coated by an alignment film, which aligns liquid crystal in a chosen direction on surface; liquid crystal is filled between the alignment films; a sealing is tightly made around the entire edge clearance between the substrates so that the liquid crystal may not be leaked therethrough; and a polarization plate is arranged often on the surface of the substrate where no alignment film is formed.
The liquid crystal display device of such a basic structure is based on any of the following five display systems:
(a) Twisted nematic field effect type display system, PA1 (b) Induced birefringence field effect type display system, PA1 (c) Dynamic scattering type display system, PA1 (d) Guest-host dichromatic display system, and PA1 (e) Orientation-vibration type display system, and the system (a) is widely utilized. PA1 (a) Obliquely vapor-deposited film of silicon oxide, etc., PA1 (b) A surface-treating agent film, or a thermosetting, polymeric film of straight chain polymer, epoxy resin or the like, the film being subjected to rubbing treatment (U.S. Pat. Nos. 3,991,241 and 3,961,843, and Japanese Laid-open Patent Application No. 96043/77), PA1 (c) A highly heat-resistance polyimide film subjected to rubbing treatment (U.S. Pat. No. 3,994,567), and PA1 (d) Glass substrate itself, subjected to rubbing treatment. PA1 (a) The obliquely vapor-deposited film of silicon oxide, etc. is different in orientation ability, depending upon type of the liquid crystal used, and no orientation is made at all in some liquid crystal. Thus, various types of liquid crystals cannot be used by mixing so as to improve a temperature characteristic and an electro-optical characteristic of liquid crystals, especially, a visual field angle characteristic is a little poor. PA1 (b) In the case of a surface-treating agent film, or a thermo-setting polymeric film of straight chain polymer, epoxy resin, or the like, an orientation ability is lowered, when a fusion sealing or sealing operation is carried out by heating an organic or inorganic fusion sealing agent or sealing compound. PA1 (c) Since the polyimide film is yellowish brown, a display ground is not clear, and such is not preferable especially for the guest-host type dichromatic display system, because a color display is required therein. Furthermore, a domain due to an orientation discontinuation is liable to be induced at display segment edge by electric field after the treatment at a high temperature, for example, 450.degree. C. PA1 (d) In the glass substrate itself, subjected to the rubbing, an orientation ability is lowered by the heating at the fusion sealing or sealing operation. PA1 --(CH.sub.2).sub.n --OH (n=1-5) hydroxyalkyl group, PA1 --(CH.sub.2).sub.n --SH (n=1-5) mercaptoalkyl group, PA1 --(CH.sub.2).sub.n --X (n=1-5, X=Cl, I, Br, or F) haloalkyl group, PA1 --(CH.sub.2).sub.n --NH.sub.2 (n=1-5), aminoalkyl group, ##STR2## the balance being the group specifically defined, referring to said R (which is not susceptible to cross-linking reaction), thereby forming a film.
The following four alignment films are employed for the liquid crystal display device:
However, all of these alignment films have the following disadvantages: